A major barrier to the growth and expansion of the consumer or home connectivity market ("consumer market"), particularly with respect to the ability easily to transmit video and audio signals throughout the home for the purpose of expanding access to a home entertainment system, as well as to media services such as satellite, cable, and telephone services from the outside Service Providers, has been the problem of internal wiring. This in turn results in a barrier to the creation of a cost-effective "smart home." In the consumer market, the primary issue limiting growth has been the diversity of signals that must be transmitted and the specialized requirements associated with the transmission of each type of signal. As a result of these various requirements, installation of smart home wiring necessarily includes a variety of cables, each with its own particular performance, termination, and installation problems. Due to the wide range of signals and the expertise needed to install the cabling, the consumer connectivity market has been limited to the domain of specialized sales, installation and retail operations. Because of the specialization of skills and tools required for the installation process, the cost of installation as either a retrofit to an existing site or as an original part of a new home is great enough that this market remains somewhat of a niche market, representing only the tip of the iceberg of the interest and demand of the consumer market. To become a truly significant market, this wiring problem must be solved to the point of permitting home installation and use by the individual consumer. Ideally, the technology must be simple enough to be mass marketed through retail outlets.
In addition to the consumer market, the office-place would benefit from technology that would enable computer images, referred to as red, green and blue ("RGB") or video graphics adapter ("VGA") signals, and audio to be transmitted throughout the office without the need for installing a variety of additional cables and wiring. One application for such technology would be the ability to permit someone else in the office building to view the output of another person's computer monitor on his own monitor, while enabling a hands-free voice intercom for discussion of same. This would enable both parties to view the same monitor output in real time. The "viewer" would be able to watch the other party's mouse movements, cursor activity, typing, and such, just as if they were standing behind the person and looking over the shoulder. At the present time, the above-described objectives could be achieved through use of a computer information network; however, this would be considered by most to be a questionable use of valuable network time. In particular, if a first user wants to obtain a copy of a document a second user is working on, the first user must download the document through the network server, in which case a copy of the document exists on the first user's computer, which may be undesirable for security reasons, and the second user cannot access the document until it is closed by the first user.
Alternatively, specialized cabling could be installed for achieving the aforementioned objectives. However, the installation of the necessary wiring would be extremely expensive, not to mention time consuming. Moreover, older buildings typically will not be able to withstand the added weight of the additional cables and wiring, in which case existing wiring must be removed before the new wiring can be installed, resulting in a great deal of added expense. Clearly, neither of these are acceptable results.
Another application that is presently implemented only through the installation and use of specialized wiring is teleconferencing, which is presently accomplished through a mobile teleconferencing system or a specialized room or site, in which case the hardware and outside interface equipment are not located in a secure and electronically proper room. Clearly, it would be beneficial to be able to have the hardware and interface equipment located in a dedicated, secure room remote from the location in which the teleconference is actually taking place.
Other areas in which it would be beneficial to have an uncomplicated way to distribute video data and audio signals include education and training applications, medical and scientific image distribution, and industrial applications.
Prior art techniques for enabling the transmission of wide bandwidth signals through copper cable has been to employ balanced mode transfer techniques, wherein two dedicated conductors are required to transmit each signal. Therefore, the number of conductors required to transmit M signal channels is 2M. Using this technique, four conductors are wound together in an opposite mode pattern as a single cable and the two virtual ground planes generated by the cable configuration are used to isolate the signal pairs. FIG. 1 illustrates a cable 108 configured in such a manner. As shown in FIG. 1, the components A+, A-, of a first balanced mode signal A are respectively applied to a first pair of conductors 110a, 110b, thereby creating a virtual ground plane 112. The components B+, B-, of a second balanced mode signal B are respectively applied to a second pair of conductors 114a, 114b, and create a virtual ground plane 116. It should be noted that the first pair of conductors 110a, 110b, are positioned such that they lie in the virtual ground plane 116, while the second pair of conductors 114a, 114b, are positioned such that they lie in the virtual ground plane 112. In this manner, energy occurring in the virtual ground plane of one of the signals is not induced into the energy transfer of the other. In other words, conductor pairs 110a, 110b, and 114a, 114b, and the respective signals carried thereon are electrically isolated from one another.
Clearly, the prior art technique illustrated in FIG. 1 suffers certain deficiencies, not the least of which is the high conductor-to-signal ratio, making the technique costly and inefficient. Moreover, each cable is capable of carrying only two signal channels. To carry three signal channels, therefore, an additional conductor pair must be installed. This can be accomplished by using three individual shielded twisted pair cables using the shield for inter-channel isolation. Unfortunately, this solution, while conceptually simple, is expensive, cumbersome, and, because it requires the installation of additional cables, labor intensive An alternative would be to add two additional conductors to the cable 108 of FIG. 1; however, the addition of conductors in this manner inhibits the use of the virtual ground planes created by the conductor pairs to isolate the signals from one another, as the virtual ground planes are generated in the wrong location to effectively isolate the pairs. In other words, in a six-conductor arrangement, the conductors cannot be arranged such that each pair lies in the virtual ground plane of another pair, making this so-called "solution" practically ineffective.
Therefore, what is needed is a low-cost, simple technique for enabling the transfer of high bandwidth analog or digital data over cable lengths up to and greater than 1000 feet.